This invention relates to installation of a cured in place liner by pulling a resin impregnated liner into the existing conduit, and inverting a resin impregnated inflation bladder with air and curing the resin with continuous flow-through of steam without loss of pressure and to the apparatuses for practicing the method. The method and apparatuses are particularly well suited for installing medium to large diameter cured in place liners.
It is generally well known that conduits or pipelines, particularly underground pipes, such as sanitary sewer pipes, storm sewer pipes, water lines and gas lines that are employed for conducting fluids frequently require repair due to fluid leakage or deterioration. The leakage may be inward from the environment into the interior or conducting portion of the pipelines. Alternatively, the leakage may be outward from the conducting portion of the pipeline into the surrounding environment. In either case, it is desirable to avoid this leakage.
The leakage may be due to improper installation of the original pipe, or deterioration of the pipe itself due to normal aging or to the effects of conveying corrosive or abrasive material. Cracks at or near pipe joints may be due to environmental conditions such as earthquakes or the movement of large vehicles on the overhead surface or similar natural or man made vibrations, or other such causes. Regardless of the cause, such leakage is undesirable and may result in waste of the fluid being conveyed within the pipeline, or result in damage to the surrounding environment and possible creation of a dangerous public health hazard. If the leakage continues it can lead to structural failure of the existing conduit due to loss of soil and side support of the conduit.
Because of ever increasing labor, energy and machinery costs, it is increasingly more difficult and less economical to repair underground pipes or portions that may be leaking by digging up and replacing the pipes. As a result, various methods had been devised for the in place repair or rehabilitation of existing pipelines. These new methods avoid the expense and hazard associated with digging up and replacing the pipes or pipe sections, as well as the significant inconvenience to the public. One of the most successful pipeline repair or trenchless rehabilitation processes that is currently in wide use is called the Insituform® Process. This Process is described in U.S. Pat. Nos. 4,009,063, 4,064,211 and 4,135,958, all the contents of which are incorporated herein by reference.
In the standard practice of the Insituform Process an elongated flexible tubular liner of a felt fabric, foam or similar resin impregnable material with an outer impermeable coating that has been impregnated with a thermosetting curable resin is installed within the existing pipeline. Generally, the liner is installed utilizing an inversion process, as described in the later two identified Insituform patents. In the inversion process, radial pressure applied to the interior of an everted liner presses it against and into engagement with the inner surface of the pipeline. However, the Insituform Process is also practiced by pulling a resin impregnated liner into the conduit by a rope or cable and using a separate fluid impermeable inflation bladder or tube that is everted within the liner to cause the liner to cure against the inner wall of the existing pipeline. Such resin impregnated liners are generally referred to as “cured-in-place-pipes” or “CIPP liners” and the installation is referred to a CIPP installation.
The CIPP flexible tubular liners have an outer smooth layer of relatively flexible, substantially impermeable polymer coating the outside of the liner in its initial state. When everted, this impermeable layer ends up on the inside of the liner after the liner is everted during installation. As the flexible liner is installed in place within the pipeline, the pipeline is pressurized from within, preferably utilizing an inversion fluid, such as water or air to force the liner radially outwardly to engage and conform to the interior surface of the existing pipeline.
Typically, an inversion tower is erected at the installation site to provide the needed pressure head to evert the liner or a bladder. Alternately, an inversion unit as shown and described in U.S. Pat. Nos. 5,154,936, 5,167,901 (RE 35,944) and U.S. Pat. No. 5,597,353, the contents of which are incorporated herein by reference. Cure may be initiated by introduction of hot water into the everted liner through a recirculation hose attached to the end of the everting liner. Inversion water is recirculated through a heat source such as a boiler or heat exchanger and returned to the inverted liner until cure of the liner is complete. The resin impregnated into the impregnable material is then cured to form a hard, tight fitting rigid pipe lining within the existing pipeline. The new liner effectively seals any cracks and repairs any pipe section or pipe joint deterioration in order to prevent further leakage either into or out of the existing pipeline. The cured resin also serves to strengthen the existing pipeline wall so as to provide added structural support for the surrounding environment.
When tubular cured in place liners are installed by the pull in and inflate method, the liner is impregnated with resin in the same manner as the inversion process and positioned within the existing pipeline in a collapsed state. A downtube, inflation pipe or conduit having an elbow at the lower end typically is positioned within an existing manhole or access point and an everting bladder is passed through the downtube, opened up and cuffed back over the mouth of the horizontal portion of the elbow. The collapsed liner within the existing conduit is then positioned over and secured to the cuffed back end of the inflation bladder. An everting fluid, such as water, is then fed into the downtube and the water pressure causes the inflation bladder to push out of the horizontal portion of the elbow and cause the collapsed liner to expand against the interior surface of the existing conduit. The inversion of the inflation bladder continues until the bladder reaches and extends into the down stream manhole or second access point. At this time the liner pressed against the interior surface of the existing conduit is allow to cure. Cure is initiated by introduction of hot water into the inflation bladder that is circulated to cause the resin in the impregnated liner to cure.
After the resin in the liner cures, the inflation bladder may be removed or left in place in the cured liner. If the inflation bladder is to be left in place, the bladder will generally be one that has a relatively thin resin impregnable layer on the inside of the impermeable outer layer. In this case, the impregnable layer after inversion will cause the bladder to adhere to the resin impregnated layer of the liner as is well known in the art. At this time, entry into the manhole or access point is required to open the liner to release the water used to inflate the bladder and to cut off the ends extending into the manholes. When the inflation bladder is to be removed, it may be removed by pulling at the evasion end on a holdback rope attached to the trailing end of the inflation bladder used to control the speed of the inversion. This is generally done after puncturing the bladder at the receiving end to release the water used to evert the bladder and initiate the resin cure. Finally, the downtube can then be removed and service can be reconnected through the lined pipeline. If intersecting service connections are present, they would be reopened prior to resumption of service through the lined pipeline.
In the existing water inversion process utilized by the Insituform Process, the liner is everted using cold water. After the liner is fully everted in the existing conduit, heated water is circulated through a lay flat tube connected to the everting face of the liner. The hot water is circulated during the cure cycle. In medium and large diameter lines as the liner diameter increases the volume of water required for inversion increases dramatically. All the water used to inflate the liner—whether everted or pulled-in-and-inflate—must be heated during the heating and cure cycle. In addition, once the cure is complete the cure water must be cooled either by addition of cold water or continued circulation until the cure water is at a temperature that may be released into the down stream conduit after the liner is cut at the end of the conduit or pump out the cure water from the cured liner and haul to an acceptable disposal system.
The major disadvantage to the use of these apparatuses with water is the quantity and availability of the inverting water. Water must be heated typically from 55° F. to 180° F. in order to affect the cure, and then cooled by the addition of more water to 100° F. before being released to an acceptable disposal system.
This disadvantage may be overcome by using air in lieu of water to create the inverting force. Once the impregnated liner is fully inverted, it then can be cured with steam. Although water is necessary to produce steam, the quantity of water in the form of steam is only 5-10% of that required for water inversion, cure and cool down. This means that steam can be used for curing even if water is not readily available on site. This drastic reduction in the quantity of water is the result of the higher energy available from one pound of water in the form of steam versus one pound of heated water. One pound of steam condensing to one pound of water gives off approximately 1000 BTUs while one pound of water gives off only one BTU for each degree in temperature drop. This reduced water requirement plus virtual elimination of the heat up cycle greatly reduces cure cycle and installation time.
With this apparent advantage in using air inversion and steam cure why has the industry been slow to abandon water inversion and hot water cure?
When water is used to invert the resin-impregnated liner, the uninverted portion of the liner from the inverting nose to the inverting apparatus is buoyed up by a force equal to the quantity of water displaced by the liner. In the case of CIPP liners, this mean the effective weight of the liner is substantially reduced, as is the force necessary to pull the uninverted liner forward to the inverting nose. When air is used to create the inverting force, the uninverted liner lies on the bottom of the pipe and the air pressure acting on the inverting nose of the liner must pull the full weight of the liner forward.
Three forces must be over come to invert a CIPP liner no matter what is used to create the inverting energy. These forces are:
1. Force required to invert the liner (turn liner inside out). This force varies by liner thickness, material type and relation of liner thickness to diameter.
2. The force necessary to pull the liner from the inverting apparatus to the inversion nose.
3. The force necessary to pull the liner through the inverting apparatus.
Force number one (1) above is generally the same for both air and water inversions.
Force number two (2) varies greatly between air and water and can limit the length of air inversions. There is limit on how much pressure can be used to invert a liner without adversely affecting the quality of the installed CIPP liner and/or damaging to the existing conduit. A lubricant can be used for both water and air inversion to reduce the required pulling force.
Force number three (3) can vary based on the apparatus design. In most apparatus presently in use, the force required to pull the liner through the apparatus will increase when either or both forces one and two increase. This is caused by the fact that in order to increase available inversion energy, typical apparatus in use today restrict loss of pressurized fluid from the pressure chamber below the liner entry point into the apparatus and the cuff and banded end of the liner being inverted. This restriction is typically accomplished by increasing the air pressure in a pneumatic sphincter gland, or by using a gland that is energized by the inverting fluid. The movement inward in typical cases is restricted by the gland material and compression of the inverting CIPP liner. This in turn causes an increase on the friction between the inverting CIPP liner and gland.
As an alternative, use of steam has been proposed in view of the energy it carries. The use of air to inflate an inflation bladder and flow-through steam has been disclosed in Insituform U.S. Pat. Nos. 6,708,728 and 6,679,293, the contents of which are incorporated herein by reference. The processes disclosed in these recently issued patents utilize pull in and inflate technology and are currently in use for small diameter liners. They provide advantages over water inversion for these size liners. Moreover, use of a purifying canister disclosed in these patents is not suitable for medium and large diameter liners. Medium size liners are those between about 21 and 45 inches in diameter. Large diameters are those in excess of about 45 inches in diameter.
While the existing methods utilizing hot water to cure have various advantages noted above, the shortcomings tend to increase energy and labor costs as well as involving a significant use of water that may have styrene entrained due to the type of resins typically used. Accordingly, it is desirable to provide a rehabilitation method suitable for medium and large diameter CIPP liners, wherein the liner is inflated by a resin impregnated inflation bladder having an integral air/steam exhaust pipe with air and the resin is cured by steam flow-through, to take advantage of the energy available in the steam to provide an installation method which is faster and more efficient economically than various rehabilitation methods currently practiced.